227 research outputs found
Comment on "Two Foreshock Sequences Post Gulia and Wiemer (2019)" by Kelian Dascher-Cousineau, Thorne Lay, and Emily E. Brodsky
No full textISSN:0895-0695ISSN:1938-2057ISSN:1938-205
Time-Space Evolution of the Groningen Gas Field in Terms of b-Value: Insights and Implications for Seismic Hazard
No full textThe Groningen gas field, located in the northeast of The Netherlands, is the Europe's larg-est onshore gas field. It was discovered in 1959 and production started in 1963: Continuous production leads to reservoir compaction and subsidence, gradually loading preexisting fault and induced seismicity that started about 30 yr into the production. The seismic hazard and risk related to the induced seismicity is determined not only for the rate of activity, but it is also equally influenced by the relative size distribution of the seismicity-the b -value. I reanalyze the spatial and temporal evolution of the b -value in the field using an alternative approach to overcome magnitude in completeness heterogeneity, and link it to the evolution of fault loading and subsidence. Spatial var-iations of b -values are found to vary between 0.61 and 1.3, with the lowest observed values observed in the location of the 2012 M 3.6 Huizinge earthquake. In the last 10 yr, the mapped b -values are more homogeneous throughout the field. The spatial and temporal evolution of the b -value in the field in this study is shown to be quite com-plex, and systematically linked it to the evolution of fault loading, absolute compaction, and the rate of compaction-an important finding that offers new insights into hazard reduction and mitigation strategies of extraction relation-induced seismicity. Compaction rates below 2 mm/yr are not correlated to seismicity above M 2.0 in the history of the field, suggesting that low-volume production may be safer than that previously assumed
Detection of quarry and mine blast contamination in European regional catalogues
No full textSeismic catalogues often include man-made contaminations, that range from the changes in seismic networks operating in the region to the different processing of the data and to the inclusion of quarry explosions and marine shots. For example, the installation or closure of seismic stations produce an increase or a decrease in the detection of small events, whilst quarry blasts or mine explosions artificially enrich catalogues. Despite network operators’ best efforts to identify quarry blasts, it is easy to find these events in a catalogue, whereas the separation between explosion events and tectonic ones is a difficult task.
Detection and removing of artificial events from a seismic catalogue should be the
preliminary step in any analysis of statistical seismology.
Wiemer and Baer (BSSA, 2000) proposed an algorithm, based on a statistical
criterion, to identify and remove quarry explosions from catalogues. It is based on
the observation that quarry blasts generally take place during daytime hours: the areas with a high ratio of daytime and night-time events are likely to be regions with quarry activity.
In the first part of this work (Gulia, NH, 2010) we have modified the method and then tested it, using both a synthetic and a regional catalogue; in the second part the
procedure has been applied to some of the European regional catalogues available on
line.
The comparison between the results obtained and the location of known quarries and mines for the analyzed catalogues confirms both the presence of non-natural events in seismic catalogue and the reliability of the methodology in identifying mining areas.PublishedMontpellier5.2. TTC - Banche dati di sismologia strumentaleope
Detection of quarry and mine blast contamination in European regional catalogues
No full textThe presence of quarry and mine blasts in seismic catalogues is detected using
the Wiemer and Baer (Bull Seism Soc Am 90(2):525–530, 2000) algorithm. The procedure
is based on the observation that quarry blasts generally take place during daytime hours:
the areas with a high ratio of daytime and night-time events are likely to be regions with
quarry activity. In the first part of this work we have tested the method, using both a
synthetic and a regional catalogue; in the second part the procedure has been applied to
some of the European regional catalogues available on line. The comparison between the
results obtained and the location of known quarries and mines for the analysed catalogues
confirms the reliability of the methodology in identifying mining areas
Contamination of frequency-magnitude slope (b-value) by quarry blasts: An example for italy
No full textArtifacts often affect seismic catalogs. Among them, the presence of man-made contaminations such as quarry blasts and explosions is a well-known problem. Using a contaminated dataset reduces the statistical significance of results and can lead to erroneous conclusions, thus the removal of such nonnatural events should be the first step for a data analyst. Blasts misclassified as natural earthquakes, indeed, may artificially alter the seismicity rates and then the b-value of the Gutenberg and Richter relationship, an essential ingredient of several forecasting models. At present, datasets collect useful information beyond the parameters to locate the earthquakes in space and time, allowing the users to discriminate between natural and nonnatural events. However, selecting them from webservices queries is neither easy nor clear, and part of such supplementary but fundamental information can be lost during downloading. As a consequence, most of statistical seismologists ignore the presence in seismic catalog of explosions and quarry blasts and assume that they were not located by seismic networks or in case they were eliminated. We here show the example of the Italian Seismological Instrumental and Parametric Database. What happens when artificial seismicity is mixed with natural one?
Din ta’ Sidek l-Għajta!
No full textĠabra ta’ poeżiji u proża li tinkludi: Tinżilx, Ja Xita! ta’ Dun Frans Camilleri – Friefet ta’ Wallace Gulia – Sunetti tal-Gwerra ta’ Erin Serracino-Inglott – Ġawhar ta’ Ħrejjef ta’ R. M. B. – Tifkiriet ta’ Wallace Gulia – Uganda ta’ S. Gatt – Din ta’ Sidek l-Għajta!N/
Review of Baronio e le sue fonti, ed. L. Gulia
No full textNow also available online at: http://www.perspectivia.net/content/publikationen/qfiab/90-2010/0527-0703.
Complete title of reviewed work: Baronio e le sue fonti. Atti del Convegno internazionale di studi, ed. Luigi Gulia, Sora 2009
Pensjonant
No full textĠabra ta’ poeżiji u proża li tinkludi: L-aħħar tas-sena ta’ Wallace Ph. Gulia – Pensjonant ta’ G. A. Cilia.peer-reviewe
Erġ’ibda għidli l-ħrejjef
No full textĠabra ta’ poeżiji u proża li tinkludi: Iżmerija ta’ F. Mangion – Ftietaq ċkejknin ta’ Ġer. Azzopardi – Bewstek ta’ Joseph Sciberras – Zorro ta’ J. P. Vassallo – Bħall-ward ta’ Joseph Sciberras – Lil ommi mejta ta’ Wallace Ph. Gulia – X’inhija l-ħajja ta’ Michael Agius – Xewqat ta’ Francis P. Mifsud – Dan il-programm ta’ Oliver Friggieri – Erġ’ibda għidli l-ħrejjef ta’ Oliver Friggieri.peer-reviewe
Asperity-based earthquake likelihood models for Italy
No full textThe Asperity Likelihood Model (ALM) hypothesizes that small-scale spatial variations in the b-value of the Gutenberg-Richter relationship have a central role in forecasting future seismicity. The physical basis of the ALM is the concept that the local b-value is inversely dependent on the applied shear stress. Thus low b-values (b < 0.7) characterize locked patches of faults, or asperities, from which future mainshocks are more likely to be generated, whereas high b-values (b > 1.1), which can be found, for example, in creeping sections of faults, suggest a lower probability of large events. To turn this hypothesis into a forecast model for Italy, we first determined the regional bvalue (b = 0.93 ±0.01) and compared it with the locally determined b-values at each node of the forecast grid, based on sampling radii ranging from 6 km to 20 km. We used the local b-values if their Akaike Information Criterion scores were lower than those of the regional b-values. We then explored two modifications to this model: in the ALM.IT, we declustered the input catalog for M ≥ 2 and smoothed the node-wise rates of the declustered catalog with a Gaussian filter. Completeness values for each node were determined using the probability-based magnitude of completeness method. In the second model, the hybrid ALM (HALM), as a «hybrid» between a grid-based and a zoning model, the Italian territory was divided into eight distinct regions that depended on the main tectonic regimes, and the local b-value variability was thus mapped using the regional b-values for each tectonic zone. © 2010 by the Istituto Nazionale di Geofisica e Vulcanologia
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